Catalytic Conversion of High Density Polyethylene (HDPE) to Transport Fuel

Abstract

As the consumption of plastic is increasingly becoming high due its positive impact on our lives, the massive amount of wastes it results is creating serious environmental glitches. Thus, this work is aimed at addressing some of these challenges by converting the plastic waste in to valuable products using chemical approach. HDPE polymer was catalytically converted using pure sulphated zirconia, S-ZrO₂ (Cat A) and CaC₂/S-ZrO₂ (Cat B). The TGA result shows that both catalysts had excellent activities, where the onset temperature for Cat A was less than 300^OC and about 420^oC for Cat B. But for Cat A, more than 90% conversion was achieved at 460^oC compared to only 3% conversion at 460^OC for polymer only. Both catalysts showed efficient polymer conversion to hydrocarbon products with 100% conversion achieved at their optimum temperatures. Cat A gives 38% liquid yield with significant aromatic component (34%) whereas Cat B gives liquid yield of 66% containing62% olefinic and 34% naphthenic and paraffinic compounds. The carbon number distribution of the fuel from both catalysts was in the range of C8-C12, which is within the gasoline range, indicating possible usage of the oil as transport fuel. The proposed reaction mechanism shows that both Cat A and Cat B obeys carbenium ion mechanism. However, Cat A supports dehydrogenation, which led to aromatisation of carbenium ion intermediates that gave rise to high aromatic content in the liquid product. Cat B showed a better property to be used for catalytic degradation of plastic waste to fuel.